Embodiments relate to generally heating, ventilation and air conditioning (HVAC) systems, and more particularly to a method and system of using condensate energy to improve HVAC system efficiency.
Air handling systems are used to heat or cool spaces. To provide appropriate air quality in occupied space, a significant amount of fresh air is brought to a building (e.g., 25 m3 h occ). This fresh air represents significant part of the thermal load of the building. This is particularly true if the air outside the building has high enthalpy content (hot and humid). The same amount of the air is extracted from the building. Extracted air has moderate dry bulb temperature and humidity (relatively low enthalpy content). Fresh air is thermally treated (cooled) and often re-heated before being supplied to an occupied space. This treatment allows for supplying air with a specified temperature and humidity level. Air treatment is conventionally provided by air handling units that include air movers (e.g., fans) and heat exchangers (water to air heat exchangers) to cool or heat the air. Usually the media to cool or heat the air is cold or hot water, with the cold water being cooled by chillers.
During the process of cooling the air, a significant amount of moisture can be removed to reduce the absolute humidity of the air. This humidity condensate on a cooling cod is collected in a condensate pan and rejected outside of the building. The amount of water removed from the air depends on fresh air relative humidity and dry bulb temperature. Given the fact that fresh air brought into the building is hot and the extracted air is colder, there is potential of exchanging energy between the two streams of the air (fresh air and extracted air). This energy exchange may be realized by air/air heat exchanger (e.g., a plate type heat exchanger). Application of such a heat exchanger will decrease temperature of fresh air and increase temperature of rejected air. By application of such a solution, overall energy of air conditioning system may be significantly reduced (10%).
There are other methods to exchange energy between the two streams of the air (extracted and fresh air). Those methods apply an enthalpy wheel to perform the heat exchange. An enthalpy wheel allows not only reduced temperature of fresh air but also a reduction of absolute humidity. Application of an enthalpy wheel is often more time expensive than a plate heat exchanger, but is also more efficient from an energy saving point of view.
While the existing air heat exchangers in air handling units work well for their intended purposes, improvements to system efficiency would be well received in the art.